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Prime+reversal= prime (Posted on 2014-03-04) Difficulty: 2 of 5
Find the smallest prime which can be represented as sum of a prime and its reversal.

See The Solution Submitted by Ady TZIDON    
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Solution a post mortem d1 solution Comment 4 of 4 |
Clearly, if one wants to solve it at first glance, - one would begin testing numbers of a 2?1 structure by choosing a prime one and then trying 2?1*1?2 -  if it's prime - stop. Solved.
No - continue with 2?7.
Ok: 201 not a prime;  211+112=323 not a prime; 221+122=343 not a prime; 231 not a prime;  241+142=  a prime number, smallest, ANSWER.
Conclusion - it always pays to try the "guessing process" at least for a while.

  Posted by Ady TZIDON on 2016-12-10 02:23:54
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